Bike keeps cutting out when changing down to lower gear, junctions, roundabouts ect, warm bike up before ride, happens after about 5/6 miles, had bike about 6mths been fine upto 2 weeks ago

SOURCE: engine clutch mess

Check your kick stand sensor if it's unplugged then there is your problem. If it's still plugged in then the sensor might be gone. The sensor shuts the bike down if you try to take off when the kick stand is down. you can bypass the sensor by jumping the two wires before the sensor with a piece of wire connecting the two leads together. doing so will allow the bike to be put into gear with the kick stand down so always check it so you won't have an accident. good luck and get out ridding!

SOURCE: backfire

Anna14 is right with the air leak,this can also be a misadjusted or faulty throttle position sensor or defective CDI Unit or a lean feul mixture.

SOURCE: Battery will not keep a charge.

Get a 2 amp charger and charge the battery fo 3 hours or so. While the battery is charging,check the fuses and check the wiring harness connections between the flywheel and the battery.

Start the bike and rev it up. Use a DC voltmeter to check the battery voltage while running. The voltmeter should read 14+ volts. If not then there may be a problem with the stator.

Pleas rate this solution. Thanks!

SOURCE: I HAVE AN OLD YAMAHA SR 125 ITS REVS GO UP AND

Remove the water trap bowl at the bottom of the petcock, (gas valve). Any water or trash in the bowl? Drain a cup of gas from the tank. Any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).

Drain the carburetor. There should be a screw on the lower side of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install a new stock NGK spark plug and try to start the engine. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the two screws on the outside throat of the carb and spray into the screw holes as well.
< < READ CLOSELY > >
Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine. Set the idle speed with the idle screw. This process should get you back on the road.

Since you mentioned uneven idle revs, be sure the carb and manifold are on tight and also tighten the cylinder and head. Air leaks can screw up the idle.

Please rate this solution. Thanks speedfreak41

SOURCE: Runs fine until bike warms up then misses

your cdi unit is suffering a from power surge try to check the output power if it is stable.